Cutting insert for a rotary cutting tool

Abstract

A cutting insert for a rotary cutting tool comprises a body of tungsten carbide, with layers of polycrystalline diamond on opposite sides of the body. The diamond layers overlap across the centre-line of the insert. The cutting insert is shaped for retention at the end of the rotary cutting tool so that the first and second sides of the cutting insert are substantially parallel to the axis of the cutting tool, and the diamond layers are offset from one another across the width of the body so that they define the lips or major cutting edges of the cutting tool.

We claim: 
     
       1. A method of manufacturing a cutting insert for a rotary cutting tool including providing a blank which comprises a body of relatively soft material and which has first and second opposed major surfaces, with first and second layers of relatively hard material on opposite sides of the body which define portions of the respective major surfaces; and cutting the blank to define a cutting insert having a body with first and second sides corresponding to the opposed major surfaces of the blank, so that the first and second sides of the insert include offset cutting edges formed from the respective first and second layers of relatively hard material. 
     
     
       2. A method according to claim 1 wherein the first and second layers of relatively hard material in the blank are offset from one another across the thickness of the blank, the method comprising cutting the blank about a line equidistant from adjacent edges of the first and second layers. 
     
     
       3. A method according to claim 2 wherein a plurality of chevron-shaped cutting inserts are cut in a nose-to-tail pattern from the blank. 
     
     
       4. A method according to claim 3 wherein the blank has a plurality of first and second strips of the relatively hard material on opposite sides thereof, the first and second strips being offset from one another across the thickness of the blank, and a plurality of rows of cutting inserts being cut from the blank about lines equidistant from adjacent edges of respective first and second strips.